1. Field of the Invention
The present invention relates to the preparation or synthesis of benzyltoluene and dibenzyltoluene compositions of low chlorine content and to the use of such compositions as dielectric liquids.
2. Description of the Prior Art
Oligomer and polyarylalkane compositions useful as dielectric liquids have been described in European Patent EP 136,230. These compositions are based essentially on benzyltoluene and dibenzyltoluene and are prepared by chlorinating toluene to benzyl chloride and then condensing the benzyl chloride with the remaining toluene via a Friedel-Crafts reaction.
In the above process, as in any process entailing a Friedel-Crafts reaction, it is not always easy to completely remove the hydrochloric acid produced by the condensation of benzyl chloride with toluene. Moreover, the benzyl chloride can also contain chlorobenzyl chloride, C.sub.6 H.sub.4 Cl--CH.sub.2 Cl, which produces chlorobenzyltoluene, C.sub.6 H.sub.4 Cl--CH.sub.2 --C.sub.6 H.sub.4 --CH.sub.3, by a Friedel-Crafts reaction.
A product (composition) which does not contain chlorine is desired for most dielectric applications. EP 306,398 describes a process for destroying organic products halogenated on the aryl carbon atoms; in particular, Example 1 illustrates the removal of the chlorobenzyltoluene present in dibenzyltoluene.
In the current state of this art, as soon as the Friedel-Crafts condensation reaction was complete, the catalyst was destroyed, for example, by washing with dilute hydrochloric acid, followed by washing with water up to the point of neutrality.